Apparatus for detecting short circuits in electrolytic cells having liquid mercury cathodes



March 23, 1965 P. DRUYLANTS FOR DETECTING SHORT 3,175,150 CIRCUITS INELECTRQLYTIC CELLS HAVING LIQUID MERCURY CATHODES APPARATUS Filed July16, 1963 INVENTOR PA UL DRUYLAN 7Z5 =ou m m muzmmmmmm 7 m m m m m M5053552m 2 nv Jr X\/ h mats #52 3375 m0 I Q I Id! 29543 f maom a? u 0 J JJMUnfibofiufim ATFORNE Y5 United States atent ()5 ice 3,175,150 PatentedMar. 23, 1965 2 Claims. (c1. 324-29 The present invention relates to anapparatus for detecting short circuits in electrochemical reaction cellsfor the electrolysis of aqueous solutions of alkali metal halides.

In such cells the short circuit obviously results from an accidentalcontact between the anode assembly and the mercury cathode. This contactmay be due to the presence of impurities on the surface of the mercury,for example, of coarse mercury or of particles of graphite; or to poorregulation of the distance between the anode and the cathode. Thebreakage of an anode can also produce such a short circuit.

Short circuits occurring in a cell with a liquid cathode are generallyfrom one of three sources;

(a) They can be due to small contact regions which are local or whichmove more or less rapidly with the dew of mercury, and which contactregions cause poor current distribution and diminution of the yield ofthe cell by bypassing some of the current intended for electrolysis.

(b) They can be due to a localized larger contact region of a certainsize which causes inconveniences like those under (a), but moreaggravated since it bypasses a substantial portion of the current of asingle anode and can in time cause heating and burning of the latter;

(0) They can be due to a low resistance and local contact region ofsmall extent. In such a case besides the results under (a) the passageof a very strong current is permitted through the area of contact,resulting in local heating of the bottom of the cell, causing it to Warpand eventually to leak.

It is obviously of primary importance to be able to detect theoccurrence of a short circuit in order to ensure the economy and safetyof electrolytic cells with mercury cathodes.

If a voltmeter is connected across the bases of two consecutive cells ofa series, any of the short circuits mentioned above will be indicated bya swinging of the needle. The amplitude of such swinging is, however,weak and very irregulatr so that it cannot be depended on to indicatethe seriousness of the short circuit. Hence a small short circuit of nopractical importance can cause a pronounced swinging of the needle whilea short circuit that causes burning of an anode or piercing of a bottom,may be hardly noticeable.

There are in commercial use very sensitive contact voltmeters whichrequire only a slight impulse to release an alarm. Such voltmeters mayhave contacts controlled by the needle of the volrneter that can beadjusted manually in such a manner that during normal service they areas close as possible to the needle of the voltmeter, ready to detectfeeble pulsations of the needle. To increase the sensitivity ofdetection, the voltmeters are con nected to the centers of the cellswith reference to their lengths so as to occupy middle positionsrelative to all the anodes. Notwithstanding its advantages, such asystem offers a serious inconvenience. First of all, the position to begiven to the contacts in order that they may remain as close as possibleto the needle is a function of the amperage in the cells and of thetemperature of the brine, for a given adjustment of the distance betweenthe anode and the cathode. When operating in this manner, the safety ofthe system depends on the man in charge of the installation because itis he who, by more or less frequent manual intervention, according tothe operating conditions, must adjust the positions of the contacts.Finally, the spreading of the scale is small because oscillations mustbe detected which are at the most only equal to 0.1 v. on a scale of 5v.

It is thus an object of the present invention to provide a new andimproved short circuit indicator for electrolylsis cells of thecharacter described.

According to one aspect of the present invention in a preferredembodiment thereof, there is first provided a plurality of electrolysiscells not necessarily of similar nature but usually of the same type.These cells are connected in series with successive anode to cathodeconnections, and the anode of the first cell is connected to a source ofpositive voltage potential whereas the cathode of the last cell isconnected to corresponding negative voltage potential. There is avoltmeter associated with each cell in the following manner: eachvoltmeter is provided with two coils capable of producing opposite fluxand correspondingly oppositely directed torques for the meter needle.One coil, called the measuring coil, is connected across the anode andcathode path of the as sociated cell. The other voltmeter coil which canalso be called reference coil, is connected across a resistance element.All resistance elements so provided pertain to a resistor which isdivided into such resistance elements by adjustable taps. Accordingly,the voltages respectively applied to reference coils pertaining tovoltmeters associated with two cells having a common anode-cathodeconnection are altered in opposite directions. There may be providedswitches to shunt the reference coil of a voltmeter, the associated cellof which has been removed from circuit for any reason.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects, and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawing in which:

There is shown a circuit network diagram constituting a preferredembodiment of the invention and provided with suitable liquids.

Turning now to the detailed description of the drawing in the figurethereof, there are shown three electrolytic cells (3,, C and C connectedin series and in between the terminals of a suitable direct currentvoltage source. The anodes and cathodes of these cells are showndiagrammatically only and comprise solid anodes A A A and mercurycathodes K K K Anode A of cell (3;, is connected to the plus pole of thevoltage source Whereas cathode K of cell C is connected to the minuspole of the voltage source. For completing the series circuit connectionthere are the following anode to cathode connections: A, to K A to K Inthe drawing, as shown by legends on cell C the mercury cathode is at thebottom with the upper surface indicated by the line below anode A andthereon is the aqueous solution being treated with its upper surfaceindicated by the line above anode A The anode is the heavy line beneaththe surface of the aqueous solution and above the surface of the body ofmercury forming the cathode.

V V and V represent voltmeters respectively associated with cells C to CEach such voltmeter has two coils b and b capable of producing oppositeflux and correspondingly oppositely directed torques for the voltmeterneedle. In case the equal flux is produced by each coil, the voltmeterindicates zero.

Coil of voltmeter V is connected across cell C i.e., between cathode Kand anode A thereof. in a similar manner, coils b of voltmeters V and Vare connected across electrolysis cells C and C respectively.

S S and S are switches for short circuiting of reference coils b of thevoltmeter. Switches S to S are individually closed whenever thecorresponding cell is removed from the circuit.

Safety fuses are represented by F and they are appropriately connectedin the circuit network.

As. will become more apparent below, coils b are the actual measuringcoils, Whereas coils b serve as reference coils. Thus, the iluX producedby coil represents a measuring flux indicative of the voltage drop inthe cell to which such coil b is connected. Coils correspondinglyproduce a reference flux as follows: The reference circuit networkprimarily comprises a resistor R made up of similar resistance elementsor sections R R R which are connected in series. Potentiometers shuntedacross small portions of adjoining resistance elements provide forsuitable adjustable taps to subdivide resistor R into these variableresistance elements primarily comprising these sections R R R it isapparent, that upon adjusting of any tap the voltage drawn from onesection is altered in opposite direction to that drawn from theadjoining section.

it can be seen specifically from the drawing, that coils b of voltmetersV V V are respectively connected across resistors R R R but using thetaps of the potentiometers between R R and R -R for completion of thereference network. Resistor R as a whole is connected between cathode Kand anode A i.e., the reference resistor is connected across all of theelectrolysis cells and, at the same time across the direct currentsource.

Use is thus being made of contact voltmeters which are equipped with twocoils Whose flux oppose each other in that the coils produce oppositelydirected torques effective at the needle as stated above. The coils arearranged in such a manner as to compare the voltage drop in each cell ofthe series of cells with the voltage drop in a respective section of areference resistor network connected to the ends of the series of cells.The sum of the voltage drops in the reference resistor is always equalto the sum of the voltage drops in the cells, so that after adjustmentof each section of the reference resistor, the needle of each voltmeteroccupies the zero position, and any deviation of the voltmeter needlefrom this position indicates and detects immediately a short circuit inthe corresponding cell.

Contact voltmeters of this kind are easily produced and, because of thetwo coils, serve to measure a difference of potential. The scale of sucha voltmeter covers a total range of 1.5 v., so that it is possible tomeasure very small changes of potential.

As is indicated in the drawing, the voltage drop in each cell C C C assensed by the measuring coil b of each voltmeter i compared with thevoltage drop in that ref erence resistor portion R R R of the resistor Rwhich is connected to the ends of the corresponding reference coil k Thereference network including resistor portions R R R, with potentiometersis connected to the ends of the series of cells C C and C in such amanner that the sum of the voltage drops in the portions R R R is ateach moment, and regardless of any other operating condition, alwaysequal to the sum of the cell volt ages. For example, if voltmeter Vshows zero, and voltmeter V shows +X volts, the voltmeter V must show Xvolts. Hence by adjusting individually and successively all of thereference resistances, whose sum remains constant, it is possible, bystarting from one point, to bring each voltmeter needle to the zeroposition. This will, in

fact, equalize all of the reference resistor portions in such a mannerthat the voltmeter-s will all remain permanently in their zero positionsduring normal operations, not even assuming that each cell carries asimilar load. This condition will prevail until the occurrence of ashort circuit in any cell. When the latter occurs, the difference due tothe voltage impulse in the defective cell will show itself on theextended scale of the voltmeter which controls tha cell and not on thenetwork of voltmeters.

For example, it may be assumed that a short circuit has occurred in celC which fact is yet unknown to the service personnel. Hence, there isnow a direct COIlI1C tion between anode A and cathode K reducing thevoltage drop applied to measuring coil [2 of voltmeter V In voltmeter Vthere will now prevail the reference flux from coil b and the voltmeterwill indicate this fact. Since electrolysis is primarily a constantvoltage process, the voltage as between cathode A and anode A is nowslightly reduced to the voltage drop prevailing across threeelectrolysis cells plus the voltage drop in the short circuited cell CCell C will now be removed from the circuit in connecting anode A tocathode K In the reference circuit network complete balance is restoredin a similar manner in closing switch S thus removing voltmeter V 2 ineffect from the measuring network. The reference voltages acrossresistances R and R are now causing balance in voltmeters V and V forzero indication.

While only three cells in series are shown, it will be evident that asmany cells as desired could be put in series in the practice of thepresent invention.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be covered by thefollowing claims.

What is claimed is:

1. Apparatus for detecting a short circuit in electrolysis cells havingliquid mercury cathodes for the electrolysis of aqueous solutions ofalkali metal halide which cells are connected in series circuitconnection, the combination comprising: a plurality of voltmeters, onefor each cell, each voltmeter having a first coil connected across theanode and cathode of its associated cell, each said voltmeter having asecond coil for producing a flux opposite to that of said first coil;and a resistor connected across said series circuit connection of saidcells and having a plurality of adjustable taps to divide said resistorinto a plurality of series connected resistors, with each such seriesconnected resistor connected across one second coil of one of saidvoltmeters by means of at least one adjustable tap.

2. In an apparatus for electrolysis of aqueous solutions of alkali metalhalides, the combination comprising: a plurality of electrolytic cellsconnected in series circuit network and to a direct current voltagesource, there being a plurality of direct anode-cathode connections ofrespectively succeeding cells, and there being a first cell and a lastcell respectively connected to the direct current voltage sourceterminals; a voltmeter associated with each cell having a first coilconnected to the anode and cathode thereof and having a second coil forproducing a flux opposite to that of said first coil; a switch for eachvoltmeter for bridging the second coil thereof; and a resistor connectedacross said series circuit network of cells and being divided into aplurality of series resistors by means of adjustable taps, each saidseries resistor being connected to the second coil of one of saidvoltmeters,

Jill! each tap adjusting in opposite directions the voltages applied tothe said second coils of those voltmeters associated with electrolyticcells having one of said direct anodecathode connections.

No reference cited.

1. APPARATUS FOR DETECTING A SHORT CIRCUIT IN ELECTROLYSIS CELLS HAVINGLIQUID MERCURY CATHODES FOR THE ELECTROLYSIS OF AQUEOUS SOLUTIONS OFALKALI METAL HALIDE WHICH CELLS ARE CONNECTED IN SERIES CIRCUITCONNECTION, THE COMBINATION COMPRISING: A PLURALITY OF VOLTMETERS, ONEFOR EACH CELL, EACH VOLTMETER HAVING A FIRST COIL CONNECTED ACROSS THEANODE AND CATHODE OF ITS ASSOCIATED CELL, EACH SAID VOLTMETER HAVING ASECOND COIL FOR PRODUCING A FLUX OPPOSITE TO THAT OF SAID FIRST COIL;AND A RESISTOR CONNECTED ACROSS SAID SERIES CIRCUIT CONNECTION OF SAIDCELLS AND HAVING A PLURALITY OF ADJUSTABLE TAPS TO DIVIDE SAID RESISTORINTO A PLURALITY OF SERIES CONNECTED RESISTORS, WITH EACH SUCH SERIESCONNECTED RESISTOR CONNECTED ACROSS ON SECOND COIL OF ONE OF SAIDVOLTMETERS BY MEANS OF AT LEAST ONE ADJUSTABLE TAP.